Catalyst-containing coating to promote rapid curing of polyurethane lacquers

ABSTRACT

Disclosed is a process for promoting the rapid curing of a two component polyurethane lacquer that has been applied to a substrate. A cure coat composition consisting of a hydroxy functional polymer such as nitrocellulose, a solvent for the polymer, and a urethane catalyst such as an organic tin compound, is applied over the polyurethane lacquer while it is in a wet or semi-dry state.

This application is a division, of application Ser. No. 07/172,615,filed 3/24/88.

FIELD OF THE INVENTION

This invention relates to a method for promoting the rapid curing of acoating of a two component polyurethane lacquer that has been applied toa substrate. This invention particularly relates to the application of acoating of a composition containing a urethane catalyst and a hydroxyfunctional polymer to the polyurethane lacquer coating to promote suchrapid curing.

BACKGROUND OF THE INVENTION

Nitrocellulose lacquer is commonly used to finish wood furniture due toits ease of application, repairability, clarity and tolerable earlyprint resistance. Print resistance is the ability to resist "printing"or "blocking", the impression left in the coating when another articleis stacked on top of the coated substrate. Blocking occurs when thefinish does not dry fast enough. Cross-linking the coating, e.g., byreaction of the free hydroxyl groups of nitrocellulose with polymericisocyanates to produce urethane linkages, will improve the mar, chemicaland early print resistance. However, an even more rapid development ofprint resistance would be desirable.

One method for overcoming this blocking problem is the use of a catalystin vapor form to accelerate the curing of paints and coatings at roomtemperature as described in British patent No. 2,142,843, British patentapplication No. 2,166,976 and Australian patent application No.62772/86. The process involves exposing a wet coating to catalystmolecules in a turbulent atmosphere. The catalyst impinges onto andpermeates the film, causing rapid polymerization to take place.

Another method for decreasing the drying and blocking time is describedin U.S. Pat. No. 4,517,222. This process involves concurrentlygenerating an atomizate of (1) a coating composition comprising ahydroxy functional compound and a polyisocyanate and (2) a carrier gasbearing a catalytic amount of a vaporous tertiary amine, mixing theatomizate and the catalyst-bearing carrier gas, and directing themixture onto the substrate to form a film.

Both of these methods require large expenditures of capital for specialequipment and the resulting coating may still lack the rapid rate ofdevelopment of block resistance that is desired.

SUMMARY OF THE INVENTION

It has now been found that rapid development of block resistance in acoating of a two component polyurethane lacquer that has been applied toa substrate can be promoted without the use of specialized equipment bycoating the lacquer while it is in a wet or semi-dry state with a curecoat composition consisting essentially of (1) from about 0.5% to about20% by weight of a hydroxy functional polymer, (2) from about 99.4% toabout 70% of a solvent for the hydroxy functional polymer and (3) fromabout 0.1% to about 10% of a catalyst for the reaction of hydroxylgroups and isocyanate groups to form urethane linkages, all percentagesbeing by weight based on the total weight of the composition.

DETAILED DESCRIPTION OF THE INVENTION

The cure coat composition of this invention is applied over a coating ofa two component polyurethane lacquer that has been applied to asubstrate. The cure coat is applied while the lacquer is in a semi-dryor preferably in a wet state to ensure adequate mixing of the cure coatwith the polyurethane lacquer. A two component polyurethane lacquer isone that is formed by the reaction of a polyol and a polyisocyanate.

When the polyurethane lacquer is applied to a substrate, solventevaporates from the lacquer film, and eddy currents form as a result ofdifferences in temperature, surface tension, and density. Evaporation ofsolvent at the film surface increases the viscosity and lowers thesurface temperature of the film. The specific gravity and surfacetension of the surface material are increased and the surface materialsinks back into the film. The lower layers of coating, rich in solventand with a low surface tension, break through the upper coating layer(which has a low solvent content), and spread over the surface, thusallowing the solvent to evaporate. This sequence of rise, spread-out,and sink is repeated continuously, and localized eddy currents areformed. It is believed that when the cure coat composition of thisinvention is applied over a coating of a two component polyurethanelacquer, the cure coat composition intermixes in the eddy currents.These currents would contain the polyurethane lacquer and also the curecoat composition. The large amount of catalyst in the cure coatcomposition promotes immediate cross-linking. If this same amount ofcatalyst were part of the polyurethane formulation, the polyurethanewould gel before it could be applied to the substrate if using a singlestream application system.

The cure coat composition of this invention can be used to promote therapid curing of a coating of any two component polyurethane lacquer.Polyols suitable for use in the preparation of a two componentpolyurethane lacquer include, but are not limited to, polyester polyols,polyether polyols, polycarbonate polyols, hydroxyacrylic resins, alkydresins and esters of ricinoleic acid and polyhydric alcohols.Polyisocyanates suitable for use in the preparation of a two componentpolyurethane lacquer include, but are not limited to, hexamethylenediisocyanate biurets, trimers of hexamethylene diisocyanate andisophorone diisocyanate trimers. For example, a typical two componentpolyurethane lacquer contains a combination of nitrocellulose and apolyester polyol as the polyol component and hexamethylene diisocyanatebiuret as the polyisocyanate component.

The combination of the polyurethane lacquer coating plus the cure coatcomposition of this invention can be applied to any surface to which thepolyurethane lacquer will adhere, e.g., metal, wood, glass and plasticsubstrates. Several coats of polyurethane lacquer are typically appliedto the substrate before application of the cure coat to the final coat.

Hydroxy functional polymers suitable for use in the cure coatcomposition of this invention include cellulose derivatives such ascellulose acetate butyrate, cellulose acetate propionate,nitrocellulose, ethyl cellulose and cellulose acetate and syntheticresins such as hydroxyacrylic resins. Nitrocellulose is preferred. Anygrade of nitrocellulose can be used. The hydroxy functional polymer ispresent in an amount of from about 0.5% to about 20% by weight, based onthe total weight of the cure coat composition.

When nitrocellulose is used as the hydroxy functional polymer, thecatalyst can be any organometallic catalyst for the reaction of hydroxylgroups with isocyanate groups to form polyurethane linkages. Suitablecatalysts include zirconium octoate, cobalt octoate, calcium octoate,manganese octoate, bismuth octoate, nickel octoate, zinc napthenate,zinc octoate, cobalt neodeconate, dibutyltin dilaurate, dimethyltindichloride, dibutyltin diacetate, dibutyltin di-2-ethyl hexoate andantimony 2-ethyl hexoate. Tin catalysts are preferred. Dimethyltindichloride is most preferred. When a hydroxy functional polymer otherthan nitrocellulose is used, tertiary amines can also be used as thecatalyst. Suitable tertiary amines include, but are not limited to,dimethylethanolamine, 1,4-diazobicyclo[2.2.2]-octanetriethylenediamine,dimethylcyclohexylamine, bis-dimethylaminoethyl ether and1,3,5-tris-(3-dimethylaminopropyl)-hexahydro-5-triazine. The catalyst ispresent in an amount of from about 0.1% to about 10% by weight, based onthe total weight of the cure coat composition.

A solvent for the hydroxy functional polymer is present in the cure coatcomposition in an amount of from about 99.4% to about 70% by weight,based on the total weight of the composition. The solvent used willdepend upon the particular hydroxy functional polymer used. The solventshould have a medium evaporation rate and an odor acceptable to theindustry, and should dissolve and intermix well when the cure coatcomposition is applied over the polyurethane lacquer. Whennitrocellulose is used as the hydroxy functional polymer, any activesolvent for nitrocellulose can be used. Suitable solvents include estersand ketones. Butyl acetate is preferred.

The drying and curing time for various substrates coated with thecombination of a two component polyurethane lacquer and the cure coatcomposition of this invention will vary depending upon parameters suchas the speed of the conveyor carrying the article through the productionline and the thickness of the polyurethane lacquer coating. The totalthickness of the polyurethane lacquer coating is preferably 2.5-3.0 milsdry. The degree of block resistance required before a coated article canbe stacked for shipping will depend upon the weight of the coatedarticle.

The cure coat composition of this invention is preferably applied to thepolyurethane lacquer coating by spraying. For this method of applicationthe viscosity of the composition is formulated to 17 sec in a #4 Fordviscometer cup. However, the cure coat composition can also be appliedby various other methods such as dipping, roll coating and curtaincoating. The thickness of the layer of the combination of thepolyurethane lacquer and the cure coat composition is preferably fromabout 2.7-3.3 mils dry.

In this specification all parts are by weight unless otherwise noted.

EXAMPLE 1

A cure coat composition for promoting the rapid curing of polyurethanelacquer coatings is prepared by dissolving 11.45 parts RS grade 1/2 secnitrocellulose (70%), IPA wet linter grade, supplied by HerculesIncorporated, in 88.25 parts butyl acetate and then adding 0.3 partdimethyltin dichloride as the catalyst.

EXAMPLE 2

A cure coat composition is prepared by dissolving 10.4 parts RS grade5-6 sec nitrocellulose (isopropyl alcohol (IPA) wet) supplied byHercules Incorporated, in a mixture of 80.1 parts butyl acetate and 7.5parts methyl amyl ketone and then adding 2.0 parts dibutyltin dilaurateas the catalyst.

EXAMPLE 3

A cure coat composition is prepared by dissolving 5.6 parts RS grade60-80 sec nitrocellulose (IPA wet) supplied by Hercules Incorporated, in92.4 parts butyl acetate and adding 2.0 parts dibutyltin dilaurate asthe catalyst.

EXAMPLE 4

A cure coat composition is prepared by dissolving 5.3 parts SS grade40-60 sec nitrocellulose (IPA wet) supplied by Hercules Incorporated, ina mixture of 68.3 parts methyl amyl ketone and 24.4 parts butyl acetate,and then adding 2.0 parts dibutyltin dilaurate as the catalyst.

EXAMPLE 5

In this example the hardness as a function of time of lacquer films withand without the application of the cure coat composition of Example 2 iscompared by means of the Konig hardness test.

The standard nitrocellulose (NC) lacquer used in test (1) has thefollowing composition (PBW =parts by weight):

    ______________________________________                                        PBW                                                                           ______________________________________                                        13.65  RS 1/4 sec nitrocellulose (70%) (Hercules                                     Incorporated)                                                          8.12   BECKOSOL 12-035 alkyd resin (60%) (Reichhold                                  Chemical Co.)                                                          3.82   CELLOLYN 104 hard resin (Hercules Incorporated)                        4.77   Dioctyl phthalate                                                      6.87   Butanol                                                                27.66  Xylene                                                                 10.31  Methyl ethyl ketone                                                    21.98  Butyl acetate                                                          2.06   EXXATE 600 solvent (Exxon Chemical Americas)                           .76    Ethanol                                                                100.00                                                                        ______________________________________                                    

The nitrocellulose/urethane lacquer used in tests (2), (3) and (5) isCSL-202 (Hercules Incorporated) and has the composition given below. Intest (5) the dibutyltin dilaurate catalyst is omitted from the cure coatcomposition of Example 2.

    ______________________________________                                        PBW                                                                           ______________________________________                                        Part A                                                                        13.8    UG RS 1/4 sec nitrocellulose (65%) (Hercules                                  Incorporated)                                                         7.2     MULTRON R221-75 PMA polyester resin (Mobay                                    Chemical Company)                                                     .02     Zinc octoate (8% zinc)                                                8.8     Toluene                                                               7.5     EXXATE 600 solvent (Exxon Chemical Americas)                          26.3    Methyl isobutyl ketone                                                30.0    Methyl ethyl ketone                                                   Part B                                                                        6.4     DESMODUR N--100 polyfunctional aliphatic                                      isocyanate (Mobay Chemical Company)                                   100.00                                                                        ______________________________________                                    

The cellulose acetate butyrate(CAB)/urethane lacquer used in test (4)has the following composition:

    ______________________________________                                        Part A                                                                        PBW                                                                           ______________________________________                                        10.5   CAB-381-0.1 (Eastman Chemical)                                         1.5    Polyol 1066 modified castor oil (Spencer                                      Kellogg Textron Incorporated)                                          23.1   Methyl ethyl ketone                                                    17.04  Butyl acetate                                                          9.28   Methyl amyl ketone                                                     22.32  Toluene                                                                5.33   Xylene                                                                 Part B                                                                        9.6    DESMODUR N--75 aliphatic polyisocyanate (Mobay                                Chemical Corporation)                                                  1.33   SPENLITE P--25-60 aliphatic urethane prepolymer                               (Spencer Kellogg Textron Incorporated)                                 100.00                                                                        ______________________________________                                    

The wiping stain used in preparing the panels for the test has thefollowing composition:

    ______________________________________                                        PBW                                                                           ______________________________________                                        17.3    #1 Industrial grade castor oil (Spencer                                       Kellogg Textron Incorporated)                                         40.7    Aromatic 150 aromatic hydrocarbon (Exxon)                             35.4    Silver bond silica extender pigment (Tammsco,                                 Inc.)                                                                 2.5     Van Dyke brown pigment (Hoover Color Corp.)                           3.1     Magnesium silicate                                                    1.0     REGAL ® 330R carbon black pigment (Cabot                                  Corp.)                                                                100.0                                                                         ______________________________________                                    

The Konig Hardness instrument used for the tests consists of pendulumsthat have two steel rocker balls that contact the dry film and rock backand forth. The number of pendulum swings (between specific angles) arecounted by an electronic counter. The oscillations of a pendulum aredampened more by a softer coating than by a harder coating. The higherthe number, the harder the coating.

The maple panels used for the Konig Hardness Development tests areprepared as follows:

1. Coat with a castor oil wiping stain and allow to dry for 30 minutes.

2. Seal with the same lacquer that is subsequently used in the testcoating and allow to dry for 30 minutes.

3. Coat with the lacquer indicated in Table 1 and dry for 30 minutes.

4. Coat with lacquer and dry for 30 minutes.

5. Apply cure coat if used (tests (3) through (5)).

The total dry film thickness on each panel is 3 mils.

Each panel is tested after 1, 2, 4, 6, 24 and 48 hours and after 5 days.The results of the tests are given in Table 1.

                  TABLE 1                                                         ______________________________________                                                     1     2      4    6    24   48   5                               Test Coating hr.   hrs.   hrs. hrs. hrs. hrs. days                            ______________________________________                                        (1) Standard NC  27    29   42   50   68   74   83                                lacquer                                                                   (2) NC/urethane   7     7    9   11   22   41   100                               lacquer                                                                   (3) NC/urethane  16    20   34   51   90   96   109                               lacquer plus                                                                  cure coat                                                                 (4) CAB/urethane 13    22   34   51   97   96   102                               lacquer plus                                                                  cure coat                                                                 (5) NC/urethane   8    10   14   18   35   58   69                                lacquer,                                                                      plus uncatalyzed                                                              cure coat                                                                 ______________________________________                                    

EXAMPLE 6

The print resistance of panels with and without the cure coatcomposition described in Example 2 is tested as described below. Printresistance is a standard test known in the art and is used to determineat what point in time a coated article can be wrapped and packaged intoa box for shipment. A given weight is applied over a 1 inch×1 inchsquare of 1/4 inch wood covered with a 1 inch×1 inch square ofcheesecloth. The weight is adjusted to coincide with the pounds persquare inch the coated article will be subjected to. The term "printfree" or "no print" applies to a coating that has been dried and thensubjected to a given psi without leaving an impression of "print". Thefour main variables involved in the test are: the time period thecoating has dried before being tested, the amount of weight used, thelength of time the test is allowed to run, and film thickness.

Maple panels for the print resistance study are prepared as described inExample 5. The formulations for the wiping stain, standardnitrocellulose lacquer, nitrocellulose/ urethane lacquer, and celluloseacetate butyrate/urethane lacquer are the same as those described inExample 5.

The cure coat is applied over the lacquer coating in tests (3) through(6). In test (4) the zinc octoate catalyst is omitted from theNC/urethane lacquer formulation. In test (5) the dibutyltin dilauratecatalyst is omitted from the cure coat composition of Example 2.

The print resistance test is run at 4 psi. The tests are started at 1,2, 4 and 8 hours after the last coat is applied and evaluations are made24 hours after the start of the test. The print rating system is asfollows:

0 --severe

2 --heavy

4 --medium

6 --slight

8 --very slight

10 --none

The results of the test are given in Table 2.

EXAMPLE 7

Test panels with and without the cure coat composition described inExample 2 are evaluated as described below to determine their resistanceto methyl ethyl ketone (MEK), which is an indication of the amount ofcross-linking that has taken place in the coating.

The maple test panels are prepared as described in Example 5. Theformulations for the wiping stain, standard nitrocellulose lacquer,nitrocellulose/urethane lacquer, and cellulose acetate butyrate/urethanelacquer are the same as those described in Example 5.

The cure coat is applied over the lacquer coating in tests (3) through(7). In tests (4) and (6) the dibutyltin dilaurate catalyst is omittedfrom the cure coat formulation. In test (5) the zinc octoate catalyst isomitted from the NC/urethane lacquer formulation.

The tests are started at 2, 4, and 8 hours, 6 days and 14 days after thelast coat is applied. Cotton balls are saturated with methyl ethylketone (MEK) and placed under a watchglass for 30 minutes. Evaluationsof the effect that MEK has on the coating are made 24 hours after thetest is stopped.

The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        (1) Standard Nitrocellulose Lacquer                                           2     hours -    completely redissolved                                       4     hours -    completely redissolved                                       8     hours -    completely redissolved                                       6     days -     completely redissolved                                       14    days -     completely redissolved                                       (2) Nitrocellulose/Urethane Lacquer                                           2     hours -    completely redissolved                                       4     hours -    completely redissolved                                       8     hours -    completely redissolved                                       6     days -     MEK resistant; slight watchglass ring                        14    days -     MEK resistant; slight watchglass ring                        (3) Nitrocellulose/Urethane Lacquer plus Cure Coat                            2     hours -    MEK resistant; slight watchglass ring                        4     hours -    MEK resistant; slight watchglass ring                        8     hours -    MEK resistant; slight watchglass ring                        6     days -     MEK resistant; slight watchglass ring                        14    days -     MEK resistant; slight watchglass ring                        (4) Nitrocellulose/Urethane                                                   Lacquer, plus Uncatalyzed Cure Coat                                           2     hours -    completely redissolved                                       4     hours -    completely redissolved                                       8     hours -    completely redissolved                                       6     days -     MEK resistant; slight watchglass ring                        14    days -     MEK resistant; slight watchglass ring                        (5) Nitrocellulose/Urethane                                                   Lacquer without Catalyst, plus Cure Coat                                      2     hours -    MEK resistant; slight watchglass ring                        4     hours -    MEK resistant; slight watchglass ring                        8     hours -    MEK resistant; slight watchglass ring                        6     days -     MEK resistant; slight watchglass ring                        14    days -     MEK resistant; slight watchglass ring                        (6) Standard Nitrocellulose                                                   Lacquer, plus Uncatalyzed Cure Coat                                           2     hours -    completely redissolved                                       4     hours -    completely redissolved                                       8     hours -    completely redissolved                                       6     days -     completely redissolved                                       14    days -     completely redissolved                                       (7) CAB/Urethane Lacquer plus Cure Coat                                       2     hours -    surface blistered, did not redissolve                        4     hours -    surface blistered, did not redissolve                        8     hours -    surface blistered, did not redissolve                        6     days -     surface blistered, did not redissolve                        14    days -     surface blistered, did not redissolve                        ______________________________________                                    

EXAMPLE 8

The relative cure rates of two nitrocellulose-urethane lacquers coatedwith a cure coat composition containing dimethyltin dichloride (DMTDC)and dibutyltin dilaurate (DBTDL) and lacquer coatings without a curecoat are compared using attenuated total reflectance infraredspectroscopy (ATR-IR) and Soxhlet extraction analysis.

The cure coat solutions are prepared by dissolving RS grade 1/2 secnitrocellulose (Hercules Incorporated) in urethane grade n-butyl acetateto give 10 weight % polymer solids. The amount and type of catalyst usedare indicated in Table 4. After adding the catalyst, the solutions arethoroughly mixed. The viscosity (#4 Ford cup) is adjusted to a sprayableviscosity of 17 sec by the addition of n-butyl acetate.

The CSL-202 nitrocellulose-urethane lacquer described in Example 5 issprayed onto four TEFLON-coated glass plates in three applications toachieve a film thickness of 2.8-3.0 mils. Five minutes after the finalapplication of the lacquer, a 0.2-0.3 mil thick layer of the cure coatformulations indicated in Table 4 is applied by spraying. The fourthplate, coated with CSL-202 but no cure coat, is used as the control. Thesame procedure is repeated using three plates coated with SUPER LIL-LACnitrocellulose-urethane lacquer (Lilly Industrial Coatings) and the curecoat formulations indicated in Table 4. The coatings are allowed to dryin a constant temperature/humidity room until they are tack-free. Aftertwo hours, the coatings are compared using ATR-IR spectroscopy todetermine whether there is a decrease in free isocyanate (NCO) groups atthe surface, an indication of the extent to which chemical cross-linkinghas taken place. The results are given in Table 4.

Soxhlet extractions are conducted 24, 48 and 168 hours hours aftercoating to determine the extent of curing. A portion of the coating ispeeled off the TEFLON-coated glass plates, placed in a pre-weighedcellulose extraction thimble and weighed. This weight is subtracted fromthe cup weight to obtain the coating weight before extraction. Thethimble is placed in the Soxhlet extractor and the lacquer film isextracted for four hours with acetone. The thimble is removed, air driedfor five minutes, dried in vacuo for one hour at 70° C., removed fromthe thimble and then weighed to give the weight % film remaining afterSoxhlet extraction. The higher the weight % lacquer film remaining afterextraction, the greater the extent of curing. The results are given inTable 4.

                  TABLE 4                                                         ______________________________________                                                     Wt %                                                                          Film                                                             Sam- Time    After   Decreasing NCO                                                                           Lacquer Cure                                  ple  (hours) Soxhlet By IR      Coating Coat                                  ______________________________________                                        1a   24      73.95   No         SUPER   0.7%                                                                  LIL-LAC DBTDL                                 1b   48      78.61   No                                                       1c   168     90.95   Yes                                                           (1 wk)                                                                   2a   24      92.38   Yes        SUPER   0.3%                                                                  LIL-LAC DMTDC                                 2b   48      90.47   Yes                                                      2c   168     94.59   Yes                                                      3a   24      92.13   Yes        SUPER   0.5%                                                                  LIL-LAC DMTDC                                 3b   48      90.46   Yes                                                      3c   168     92.22   Yes                                                      4a   24      74.01   No         CSL-202 0.7%                                                                          DBTDL                                 4b   48      78.28   No                                                       4c   168     91.33   Yes                                                      5a   24      89.86   Yes        CSL-202 0.3%                                                                          DMTDC                                 5b   48      89.82   Yes                                                      5c   168     92.60   Yes                                                      6a   24      90.64   Yes        CSL-202 0.5%                                                                          DMTDC                                 6b   48      89.14   Yes                                                      6c   168     92.73   Yes                                                      7a   24      0.00    No         CSL-202 None                                  7b   48      20.58   No                                                       7c   168     88.78   Yes                                                      ______________________________________                                    

EXAMPLE 9

The hardness as a function of time of lacquer films with and without acure coat is compared by means of the Konig hardness test described inExample 5. The cure coat formulations are made with a hydroxyacrylicresin or cellulose acetate butyrate (CAB) as the hydroxy functionalpolymer and dibutyltin dilaurate (DBTDL) or a tertiary amine (DES-PP) asthe catalyst.

A polyurethane lacquer is prepared by mixing 150 ml IMRON® polyurethaneenamel (Du Pont) and 50 ml IMRON® 192S activator (Du Pont).

The following cure coat formulations are prepared for application overthe IMRON® polyurethane lacquer.

    ______________________________________                                        Cure Coat 1                                                                    89.7 g                                                                              Butyl acetate                                                           8.3   ACRYLOID QR-999 hydroxyacrylic polyol (Rohm                                   and Haas Co.)                                                           2.0   Dibutyltin dilaurate                                                   100.0                                                                         Cure Coat 2                                                                    89.7 g                                                                              Butyl acetate                                                           8.3   ACRYLOID QR-999 hydroxyacrylic polyol (Rohm                                   and Haas Co.)                                                           2.0   DESMORAPPID PP tertiary amine catalyst                                        (Mobay Chemical Corp.)                                                 100.0                                                                         ______________________________________                                    

A CAB/urethane lacquer having the composition described in Example 5 isprepared.

The following cure coat formulations are prepared for application overthe CAB/urethane lacquer.

    ______________________________________                                        Cure Coat 3                                                                   58.6 g   Butyl acetate                                                        19.4     Methyl amyl ketone                                                   14.3     Methyl ethyl ketone                                                   5.7     CAB-381-20 cellulose acetate butyrate (Eastman                                Chemical)                                                             2.0     Dibutyltin dilaurate                                                 100.0                                                                         Cure Coat 4                                                                   58.6 g   Butyl acetate                                                        19.4     Methyl amyl ketone                                                   14.3     Methyl ethyl ketone                                                   5.7     CAB-381-20 cellulose acetate butyrate (Eastman                                Chemical)                                                             2.0     DESMORAPPID PP tertiary amine catalyst                                        (Mobay Chemical Corp.)                                               100.0                                                                         ______________________________________                                    

One coat of the IMRON® polyurethane lacquer is sprayed onto three glasstest panels. One panel is sprayed with cure coat formulation 1, anotherwith cure coat formulation 2 and the third is the control with no curecoat. Three test panels are then sprayed with the CAB/urethane lacquer.One of these panels is sprayed with cure coat formulation 3, one withcure coat formulation 4 and the third is the control with no cure coat.

The Konig hardness test is carried out at four locations on each plate.The results are given in Table 5.

                                      TABLE 5                                     __________________________________________________________________________           KONIG HARDNESS    KONIG HARDNESS                                              IMRON ® LACQUER                                                                             CAB/URETHANE LACQUER                                                DBTDL                                                                              DES-PP       DBTDL                                                                              DES-PP                                  DRY TIME                                                                             NO      CURE CURE NO      CURE CURE                                    (HOURS)                                                                              CURE COAT                                                                             COAT COAT CURE COAT                                                                             COAT COAT                                    __________________________________________________________________________    2.0    7       14   11   20      49   80                                             6       14   11   20      50   80                                             6       13   11   20      49   80                                             7       14   10   20      49   81                                      3.0    6       13   10   22      62   81                                             7       12   10   20      63   85                                             7       12   11   21      61   79                                             6       13   10   21      61   80                                      4.0    7       11   11   25      75   79                                             6       11   10   23      78   80                                             6       11   11   21      80   81                                             7       11   11   21      78   82                                      __________________________________________________________________________

EXAMPLE 10

The print resistance of panels with and without the cure coatcomposition of Example 1 is tested as described in Example 6.

A cure coat is applied over the lacquer coating in tests (3) through(5). In test (4) the dimethyltin dichloride catalyst is omitted from thecure coat formulation.

The formulations for the wiping stain and the CAB/ urethane lacquer arethe same as the ones described in Example 5.

The standard nitrocellulose lacquer used in test (1) has the followingcomposition.

    ______________________________________                                        PBW                                                                           ______________________________________                                        11.2   RS 1/2 sec nitrocellulose (Hercules                                           Incorporated)                                                          8.0    AROPLAZ ® 2575-X-60 nonoxidizing alkyd resin                              (NL Industries)                                                        3.2    CELLOLYN 104 hard resin (Hercules Incorporated)                        4.0    Dioctyl phthalate                                                      24.0   Butyl acetate                                                          8.0    Methyl ethyl ketone                                                    4.8    n-Butanol                                                              4.0    Butyl cellosolve                                                       32.8   Xylene                                                                 100.0                                                                         ______________________________________                                    

The nitrocellulose/urethane lacquer used in tests (2) through (4) isprepared by mixing 300 parts of Part A of the CLS-202 formulationdescribed in Example 5 with 20.4 parts DESMODUR N-100 polyfunctionalaliphatic isocyanate (Mobay Chemical Co.).

The print resistance test is run at 4 psi. The tests are started at 1, 2and 3 hours after the last coat is applied and evaluations are made 24hours after the start of the test.

The results of the test are given in Table 6.

                  TABLE 6                                                         ______________________________________                                        Test Coating      1 hr.    2 hrs.  3 hrs                                      ______________________________________                                        (1) Standard NC lacquer                                                                             10       10    10                                       (2) NC/urethane lacquer                                                                             0        0     2                                        (3) NC/urethane lacquer plus                                                                        10       10    10                                           cure coat                                                                 (4) NC/urethane lacquer plus                                                                        2        2     4                                            uncatalyzed cure coat                                                     (5) CAB/urethane lacquer plus                                                                       10       10    10                                           cure coat                                                                 ______________________________________                                    

EXAMPLE 11

The hardness as a function of time of lacquer films with and without theapplication of the cure coat composition of Example 1 is compared bymeans of the Konig hardness test described in Example 5. Glass panels(4×8") are used instead of maple panels. The total dried film thicknesson each panel is 3 mils.

A cure coat is applied over the lacquer coating in tests (3) through(5). In test (4) the dimethyltin dichloride catalyst is omitted from thecure coat formulation.

The wiping stain, CSL-202 nitrocellulose/urethane lacquer, CAB/urethanelacquer and standard nitrocellulose lacquer formulations are the same asthose used in Example 10.

Each panel is tested after 1, 2, 4, 6 and 24 hours and after 48 hours, 6days or 7 days. The results of the tests are given in Table 7.

                  TABLE 7                                                         ______________________________________                                        Test      1     2      4    6    24   48   6    7                             Coating   hr.   hrs.   hrs. hrs. hrs. hrs. days days                          ______________________________________                                        (1) Standard  15    22   31   41   76   --   85   --                              NC                                                                            lacquer                                                                   (2) NC/       8     10   11   12   21   47   --   119                             urethane                                                                      lacquer                                                                   (3) NC/       42    60   79   88   98   104  --   109                             urethane                                                                      lacquer                                                                       plus cure                                                                     coat                                                                      (4) NC/       5     6    9    10   15   28   --   99                              urethane                                                                      lacquer                                                                       plus                                                                          uncatalyzed                                                                   cure coat                                                                 (5) CAB/      30    54   86   98   105  116  --   116                             urethane                                                                      lacquer                                                                       plus cure                                                                     coat                                                                      ______________________________________                                    

What I claim and desire to protect by Letters Patent is:
 1. A processfor promoting the rapid curing of a coating of a two componentpolyurethane lacquer that has been applied to a substrate, said processcomprising(1) coating the polyurethane lacquer while it is in a semi-dryor wet state with a composition consisting essentially ofa. from about0.5% to about 20% of a hydroxy functional polymer, b. from about 99.4%to about 70% of a solvent for the hydroxy functional polymer, and c.from about 0.1% to about 10% of a catalyst for the reaction of hydroxylgroups with isocyanate groups to form urethane linkages, all percentagesbeing by weight based on the total weight of the composition, and (2)drying the coated polyurethane lacquer.
 2. The process of claim 1wherein the hydroxy functional polymer is nitrocellulose and thecatalyst is an organic tin compound.
 3. The process of claim 2 whereinthe catalyst is dimethyltin dichloride.
 4. The process of claim 2wherein the catalyst is dibutyltin dilaurate.